Sign languages provide a powerful tool for investigating the neurobiology and cognitive architecture of human language. For perception, these languages depend upon high-level vision and motion processing systems; for production, they require the integration of motor systems involving the hands and face. What impact does this different biological base have on language processing? How does it affect non-linguistic cognitive functions? Are the same neural systems involved? We investigate these issues by studying neurologically-intact deaf signers, focusing on a coherent set of cognitive functions implicated in the processing of sign language. We proceed along the primary lines of inquiry: I. The effects of spatialization on language. We investigate a unique aspect of sign language: the linguistic use of physical space. We will examine on-line comprehension of spatialized co- reference, the nature of linguistic use of physical space. We will examine on-line comprehension of spatialized co-reference, the nature of linguistic versus cognitive spatial categories, and the relation between spatial gestures and spatial signs. For the first time, we will investigate the representation and processing of cross-linguistic study of how different sign languages express topological spatial relations. Together, these studies will indicate how the visual-spatial modality impacts grammatical form and language processing. II. The interplay between language and visual-spatial cognition. Our proposed studies are motivated by exciting findings under the current grant which show that processing the complex spatial system of American Sign Language (ASL) exerts selective enhancement of non-linguistic visual-spatial processing. We investigate the impact of sign language use on the following cognitive functions; motion perception and analysis, the recognition and categorization of human faces and facial expressions, and visual-spatial imagery. A major goal is to determine how the language one uses can affect cognitive processes in non-linguistic domains. III. The neural bases for language and spatial cognition in deaf signers. The unusual sensory and linguistic experience of deaf ASL signers provides a natural opportunity to investigate neural plasticity and the determinants of brain organization. We will investigate cerebral specialization for sign language and its cognitive underpinnings, using standard hemifield techniques. We also propose two studies using fMRI which investigate face processing and visual imagery; fMRI will provide an exquisitely detailed picture of the brain bases for these linguistic and cognitive functions.